Elevated inputs of fine sediments to waterways impact the physical, chemical and biological structure and function of aquatic ecosystems. The two main sources of fine sediments to rivers are within-channel sources and catchment sources. Quantifying the spatial origin of fine sediments entering fluvial systems is essential for understanding fine sediment dynamics, the resulting biophysical impacts and developing priorities for restoration strategies. The Pages River, a tributary of the Hunter River in NSW, contains a sediment slug greater than 1.5km long in its lower reaches. This sediment slug prevents surface water connectivity at base flows, significantly impacting the ecology of the river, such as prevention of longitudinal fish movement.
This study used geochemical tracers to define composite sediment fingerprints from 15 source and 8 sink locations within the Pages River subcatchment. Tracers included physical characteristics, major and trace elements and stable isotopes in a discriminant function analysis to distinguish between the four major geologies as potential sources of fine sediment. A modified Hughes mixing model used 7 geochemical and physical tracers that explained 100% of the variance in sources to determine their contribution to sink sites within the trunk of the Pages River. The study found that the carboniferous conglomerate within the Warlands Creek subcatchment contributed the most fine sediment to the Pages River of any tributary or the channels of the upper Pages River. Erodible geology, high slope and altered landuse (cattle grazing) within Warlands Creek contributed to accelerated erosion and transport of fine sediments. Rehabilitation actions within Warlands Creek such as fencing of stream banks, riparian revegetation and pasture management would disproportionately improve fine sediment dynamics within the Pages River.